[mojo-edk] Add MojoWatch and MojoCancelWatch APIs

This adds MojoWatch() and MojoCancelWatch() APIs to support
efficient asynchronous handle event notifications.

BUG=590495

Review URL: https://codereview.chromium.org/1748503002

Cr-Commit-Position: refs/heads/master@{#378677}

1 files changed, 26 insertions, 0 deletions

diff --git a/mojo/edk/system/data_pipe_consumer_dispatcher.cc b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
index 1f6f079..269f8b2 100644
--- a/mojo/edk/system/data_pipe_consumer_dispatcher.cc
+++ b/mojo/edk/system/data_pipe_consumer_dispatcher.cc
@@ -21,6 +21,7 @@
 #include "mojo/edk/system/data_pipe_control_message.h"
 #include "mojo/edk/system/node_controller.h"
 #include "mojo/edk/system/ports_message.h"
+#include "mojo/edk/system/request_context.h"
 #include "mojo/public/c/system/data_pipe.h"
 
 namespace mojo {
@@ -86,6 +87,29 @@ MojoResult DataPipeConsumerDispatcher::Close() {
   return CloseNoLock();
 }
 
+
+MojoResult DataPipeConsumerDispatcher::Watch(
+    MojoHandleSignals signals,
+    const Watcher::WatchCallback& callback,
+    uintptr_t context) {
+  base::AutoLock lock(lock_);
+
+  if (is_closed_ || in_transit_)
+    return MOJO_RESULT_INVALID_ARGUMENT;
+
+  return awakable_list_.AddWatcher(
+      signals, callback, context, GetHandleSignalsStateNoLock());
+}
+
+MojoResult DataPipeConsumerDispatcher::CancelWatch(uintptr_t context) {
+  base::AutoLock lock(lock_);
+
+  if (is_closed_ || in_transit_)
+    return MOJO_RESULT_INVALID_ARGUMENT;
+
+  return awakable_list_.RemoveWatcher(context);
+}
+
 MojoResult DataPipeConsumerDispatcher::ReadData(void* elements,
                                                 uint32_t* num_bytes,
                                                 MojoReadDataFlags flags) {
@@ -474,6 +498,8 @@ void DataPipeConsumerDispatcher::OnPortStatusChanged() {
 }
 
 void DataPipeConsumerDispatcher::UpdateSignalsStateNoLock() {
+  RequestContext request_context;
+
   lock_.AssertAcquired();
 
   bool was_peer_closed = peer_closed_;